After enduring your constant gushing about your new boyfriend, Rin finally mutters bluntly,

"I couldn't care less."

His jealousy towards your new relationship had been building up for quite some time. He had harbored feelings for you for ages, but his focus on his soccer career had prevented him from expressing them or confessing. Now, however, he deeply regrets his decision, as the unmistakable signs of his jealousy are impossible to ignore.